A Step-by-Step Guide to Mosquito Electroantennography

Summary

The present article details a step-by-step protocol for successful and low noise electroantennograms in several genera of mosquitoes, including both females and males.

Abstract

Female mosquitoes are the deadliest animals on earth, claiming the lives of more than 1 million people every year due to pathogens they transmit when acquiring a blood-meal. To locate a host to feed on, mosquitoes rely on a wide range of sensory cues, including visual, mechanical, thermal, and olfactory. The study details a technique, electroantennography (EAG), that allows researchers to assess whether the mosquitoes can detect individual chemicals and blends of chemicals in a concentration-dependent manner. When coupled with gas-chromatography (GC-EAG), this technique allows to expose the antennae to a full headspace/complex mixture and determines which chemicals present in the sample of interest, the mosquito can detect. This is applicable to host body odors as well as plant floral bouquets or other ecologically relevant odors (e.g., oviposition sites odorants). Here, we described a protocol that permits long durations of preparation responsiveness time and is applicable to both female and male mosquitoes from multiple genera, including Aedes, Culex, Anopheles, and Toxorhynchites mosquitoes. As olfaction plays a major part in mosquito-host interactions and mosquito biology in general, EAGs and GC-EAG can reveal compounds of interest for the development of new disease vector control strategies (e.g., baits). Complemented with behavioral assays, the valence (e.g., attractant, repellent) of each chemical can be determined.

Introduction

Mosquitoes are the deadliest organisms on earth, claiming the lives of more than one million people per year and place more than half the world population at risk of exposure to the pathogens they transmit, while biting¹. These insects rely on a wide range of cues (i.e., thermal, visual, mechanical, olfactory, auditory) to locate a host to feed on (both plant and animal), for mating and oviposition, as well as to avoid predators at both the larval and adult stages^2,3. Among these senses, olfaction plays a critical role in the above mentioned behaviors, in particular for medium to long-r....

Protocol

1. Saline solution preparation

1. Prepare the saline in advance and store in the fridge.
2. Follow Beyenbach and Masia²⁶ to prepare the solution.
   ​NOTE: Saline recipe in mM: 150.0 NaCl, 25.0 HEPES, 5.0 glucose, 3.4 KCl, 1.8 NaHCO₃, 1.7 CaCl₂, and 1.0 MgCl₂. The pH is adjusted to 7.1 with 1 M NaOH. Do not add glucose or sucrose to the preparation at this time to increase shelf storage. Add the needed quantity to the saline right before running the EAGs (around 50 mL per experiment).

2. Odor preparation and storage

1. Prepare the odorant mixt....

Results

Electroantennography is a powerful tool to determine whether a chemical or blend of chemicals is detected by an insect antenna. It can also be used to determine the detection threshold for a given chemical using a gradual increase of concentration (i.e., dose curve response, Figure 4B). Moreover, it is useful to test the effects of repellent on the response to host-related odors²⁹.

Positive and negative controls should always be used in EAG.......

Discussion

Olfactory mediated behaviors are affected by many factors, including physiological (e.g., age, time of day) and environmental (e.g., temperature, relative humidity)³⁰. Thus, when conducting EAGs, it is essential to use insects that are in the same physiological status (i.e., monitoring for age, starving, mating)³¹ and to also maintain a warm and humid environment around the preparation to avoid desiccation. A temperature around 25 °C is ideal and 60% to 80% humidity fo.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Air table Clean Bench	TMC	https://www.techmfg.com/products/labtables/cleanbench63series/accessoriess	Noise reducer
Analog-to-digital board	National Instruments	BNC-2090A
Benchtop Flowbuddy Complete	Genesee Scientific	59-122BC	To anesthesize mosquitoes
Borosillicate glass capillary	Sutter Instrument	B100-78-10	To make the recording and references capillaries
Chemicals	Sigma Aldrich	Benzaldehyde: 418099-100 mL; Butyric acid: B103500-100mL; 1-Hexanol: 471402-100mL; Mineral oil: M8410-1L	Chemicals used for the experiments presented here
CO2	Airgas or Praxair	N/A	To anesthesize mosquitoes
Cold Light Source	Volpi	NCL-150
Disposable syringes	BD	1 mL (309628)  / 3 mL (309657)
Electrode cables	World Precision Instruments	5371
Electrode gel salt free	Parkerlabs	12-08-Spectra-360
Faraday cage	TMC	https://www.techmfg.com/products/electric-and-magnetic-field-cancellation/faradaycages	Noise reducer
Flowmeters	Bel-art	65 mm (H40406-0010) / 150 mm (H40407-0075)	One of each
GCMS vials and caps	Thermo-fisher scientific	2-SVWKA8-CPK	To prepare odorant dilutions
Glass syringes (Fortuna)	Sigma Aldrich	Z314307	For odor delivery to the EAG prep
Humbug	Quest Scientific	http://www.quest-sci.com/	Noise reducer
2 mm Jack Holder, Narrow, 90 deg., With Wire	A-M Systems	675748	Electrode holder
Magnetic bases	Kanetec	MB-FX	x 2
MATLAB + Toolboxes	Mathworks	https://www.mathworks.com/products/matlab.html	For delivering the pulses
Medical air	Airgas or Praxair	N/A	For main airline
Microscope	Nikkon	SMZ-800N
Micromanipulators Three-Axis Coarse/Fine Compact Micromanipulator	Narishige	MHW-3	x 2
Microelectrode amplifier with headstage	A-M Systems	Model 1800
Mosquito rearing supplies	Bioquip	https://www.bioquip.com/Search/WebCatalog.asp
Needles	BD	25G (305127) / 21G (305165)
Pasteur pipettes	Fisher Scientific	13-678-6A	For odor delivery to the EAG prep
PTFE Tubing of different diameters	Mc Master Carr	N/A	To connect solenoid valve, flowmeter, airline ect.
30V/5A DC Power Supply	Dr. Meter	PS-305DM
R version 3.5.1	R project	https://www.r-project.org/	For data analyses
Relay for solenoid valve	N/A	Custom made
Silver wire 0.01”	A-M Systems	782500
Solenoid valve (3-way)	The Lee Company	LHDA0533115H
WinEDR software	Strathclyde Electrophysiology Software	WinEDR V3.9.1	For EAG recording
Whatman paper	Cole Parmer	UX-06648-03	To load chemical in glass syringe / Pasteur pipette